ISL29033IROZ-T7 Datasheet, PDF (6/15 Pages) Intersil Corporation – Ultra-Low Lux, Low Power, Integrated Digital Ambient Light Sensor with Interrupt Function

ISL29033
I²C Electrical Specifications For SCL and SDA (Figure 2), unless otherwise noted, V_DD = 3V, T_A = +25°C, R_EXT = 499kΩ 1%
and 1MΩ 1% tolerance. (Continued)
PARAMETER
DESCRIPTION
CONDITION
MIN
(Note 6)
MAX
TYP (Note 6) UNIT
t_VD;DAT
Data Valid Time
t_VD:ACK
Data Valid Acknowledge Time
V_nL
Noise Margin at the LOW Level
V_nH
Noise Margin at the HIGH Level
NOTE:
9. C_b is the capacitance of the bus in pF.
0.1V_DD
0.2V_DD
0.9
µs
0.9
µs
V
V
Principles of Operation
Photodiodes and ADC
The ISL29033 contains two photodiode arrays that convert light into
current. The spectral response for ambient light sensing and
infrared (IR) sensing is shown in Figure 8 in the “Typical
Performance Curves” section on page 12. After light is converted to
current during the light signal process, the current output is
converted to digital by a built-in 16-bit Analog-to-Digital Converter
(ADC). An I²C command reads the ambient light or IR intensity in
counts.
The converter is a charge-balancing integrating type 16-bit ADC. The
chosen method for conversion is best for converting small current
signals in the presence of an AC periodic noise. A 100ms integration
time, for instance, highly rejects 50Hz and 60Hz power line noise
simultaneously. See “Integration and Conversion Time” on page 9.
The built-in ADC offers user flexibility in integration time or
conversion time. There are two timing modes: Internal Timing Mode
and External Timing Mode. In Internal Timing Mode, integration time
is determined by an internal oscillator (f_OSC) and the n-bit (n = 4, 8,
12, 16) counter inside the ADC. In External Timing Mode, integration
time is determined by the time between two consecutive I²C
External Timing Mode commands. A good balance of integration
time and resolution (depending on application) is required for
optimal results.
The ADC has I²C programmable range select to dynamically
accommodate various lighting conditions. For very dim conditions,
the ADC can be configured at its lowest range (Range 1) in the
ambient light sensing.
Low-Power Operation
Ambient Light
There are four operational modes in ISL29033: Programmable ALS
once with auto power-down, programmable IR sensing once with
auto power-down, programmable continuous ALS sensing, and
programmable continuous IR sensing. These four modes can be
programmed in series to fulfill the application needs. The detailed
program configuration is shown in “BLOCK DIAGRAM” on page 1.
When the part is programmed for ambient light sensing, the
ambient light with wavelength within the “Ambient Light
Sensing” spectral response curve in Figure 8 is converted into
current. With ADC, the current is converted to an unsigned n-bit
(up to 16 bits) digital output.
When the part is programmed for infrared (IR) sensing, the IR
light with wavelength within the “IR Sensing” spectral response
curve in Figure 8 is converted into current. With ADC, the current
is converted to an unsigned n-bit (up to 16 bits) digital output.
Interrupt Function
The active low interrupt pin is an open drain pull-down
configuration. The interrupt pin serves as an alarm or monitoring
function to determine whether the ambient light level exceeds
the upper threshold or goes below the lower threshold. Note that
the function of ADC conversion continues without stopping after
interrupt is asserted. If the user needs to read the ADC count that
triggers the interrupt, reading should be done before the data
registers are refreshed by subsequent conversions. The user can
also configure the persistency of the interrupt pin. This reduces
the possibility of false triggers, such as noise or sudden spikes in
ambient light conditions. An unexpected camera flash, for
example, can be ignored by setting the persistency to eight
integration cycles.
The ISL29033 initial operation is at the power-down mode after a
supply voltage is provided. The data registers contain the default
value of 0. When the ISL29033 receives an I²C command to do a
one-time measurement from an I²C master, it starts ADC
conversion with light sensing. It goes to power-down mode
automatically after one conversion is finished and keeps the
conversion data available for the master to fetch anytime
afterwards. The ISL29033 continuously does ADC conversion
with light sensing if it receives an I²C command of continuous
measurement. It continuously updates the data registers with
the latest conversion data. It goes to power-down mode after it
receives the I²C command of power-down.
ALS Ranges Considerations
When measuring ALS counts higher than 30000 counts on
Range 1 of the 16-bit ADC, switch to Range 2 (change [1 to 0]
bits of Register 1 from 00 to 01), and re-measure the ALS counts
and other data to change to Range 3 and Range 4. This
recommendation pertains only to applications in which light
incident on the sensor is IR-heavy and is distorted by tinted glass
that increases the ratio of infrared to visible light.
V_DD Power-up and Power Supply
Considerations
Upon power-up, ensure a V_DD slew rate of 0.5V/ms or greater.
After power-up, or if the power supply temporarily deviates from
6
FN7656.2
February 25, 2013